execve - execute program


SYNOPSIS

       #include <unistd.h>

       int  execve  (const  char  *filename, char *const argv [],
       char *const envp[]);


DESCRIPTION

       execve() executes the  program  pointed  to  by  filename.
       filename  must  be either a binary executable, or a script
       starting with a line of the form "#!  interpreter  [arg]".
       In  the latter case, the interpreter must be a valid path­
       name for an executable which is not itself a script, which
       will be invoked as interpreter [arg] filename.

       argv  is  an  array  of argument strings passed to the new
       program.  envp is an array of strings,  conventionally  of
       the form key=value, which are passed as environment to the
       new program.  Both, argv and envp must be terminated by  a
       null  pointer.  The argument vector and environment can be
       accessed by the called program's main function, when it is
       defined as int main(int argc, char *argv[], char *envp[]).

       execve() does not return on success, and the  text,  data,
       bss,  and  stack of the calling process are overwritten by
       that of the program loaded.  The program invoked  inherits
       the  calling  process's PID, and any open file descriptors
       that are not set to close on exec.  Signals pending on the
       calling process are cleared.  Any signals set to be caught
       by  the  calling  process  are  reset  to  their   default
       behaviour.   The  SIGCHLD signal (when set to SIG_IGN) may
       or may not be reset to SIG_DFL.

       If the current program is being ptraced, a SIGTRAP is sent
       to it after a successful execve().

       If  the  set-uid bit is set on the program file pointed to
       by filename the effective user ID of the  calling  process
       is changed to that of the owner of the program file.  Sim­
       ilarly, when the set-gid bit of the program  file  is  set
       the  effective  group  ID of the calling process is set to
       the group of the program file.

       If the executable is an  a.out  dynamically-linked  binary
       executable  containing  shared-library  stubs,  the  Linux
       dynamic linker ld.so(8) is called at the start  of  execu­
       tion  to  bring needed shared libraries into core and link
       the executable with them.

       If the executable is a dynamically-linked ELF  executable,
       the  interpreter named in the PT_INTERP segment is used to
       load the needed shared  libraries.   This  interpreter  is

       Linux libc version 5, or /lib/ld-linux.so.2  for  binaries
       linked with the GNU libc version 2.


RETURN VALUE

       On  success,  execve()  does  not  return,  on error -1 is
       returned, and errno is set appropriately.


ERRORS

       EACCES The file or a script interpreter is not  a  regular
              file.

       EACCES Execute  permission  is  denied  for  the file or a
              script or ELF interpreter.

       EACCES The file system is mounted noexec.

       EPERM  The file system is mounted nosuid, the user is  not
              the superuser, and the file has an SUID or SGID bit
              set.

       EPERM  The process is being traced, the user  is  not  the
              superuser and the file has an SUID or SGID bit set.

       E2BIG  The argument list is too big.

       ENOEXEC
              An executable is not in a recognised format, is for
              the  wrong  architecture,  or has some other format
              error that means it cannot be executed.

       EFAULT filename points  outside  your  accessible  address
              space.

       ENAMETOOLONG
              filename is too long.

       ENOENT The  file  filename  or a script or ELF interpreter
              does not exist, or a shared library needed for file
              or interpreter cannot be found.

       ENOMEM Insufficient kernel memory was available.

       ENOTDIR
              A  component  of  the  path prefix of filename or a
              script or ELF interpreter is not a directory.

       EACCES Search permission is denied on a component  of  the
              path  prefix  of  filename  or the name of a script
              interpreter.

       ELOOP  Too many symbolic links were encountered in resolv­
              ing  filename or the name of a script or ELF inter­
              preter.

              Executable was open for writing by one or more pro­
              cesses.

       EIO    An I/O error occurred.

       ENFILE The  limit on the total number of files open on the
              system has been reached.

       EMFILE The process has the maximum number of files open.

       EINVAL An ELF executable had more than one PT_INTERP  seg­
              ment  (i.e.,  tried  to  name  more than one inter­
              preter).

       EISDIR An ELF interpreter was a directory.

       ELIBBAD
              An ELF interpreter was not in a recognised  format.


CONFORMING TO

       SVr4,  SVID, X/OPEN, BSD 4.3.  POSIX does not document the
       #!  behavior but is otherwise compatible.  SVr4  documents
       additional  error  conditions EAGAIN, EINTR, ELIBACC, ENO­
       LINK, EMULTIHOP; POSIX does not document  ETXTBSY,  EPERM,
       EFAULT,  ELOOP,  EIO,  ENFILE,  EMFILE,  EINVAL, EISDIR or
       ELIBBAD error conditions.


NOTES

       SUID and SGID processes can not be ptrace()d.

       Linux ignores the SUID and SGID bits on scripts.

       The result of mounting a filesystem  nosuid  vary  between
       Linux  kernel  versions:  some  will  refuse  execution of
       SUID/SGID executables when this would give the user powers
       she  did  not  have  already (and return EPERM), some will
       just ignore the SUID/SGID bits and exec successfully.

       A maximum line length of 127 characters is allowed for the
       first line in a #! executable shell script.


SEE ALSO

       chmod(2), fork(2), execl(3), environ(5), ld.so(8)


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